add lkml/cc's. On 01/18, Linus Torvalds wrote: > > On Fri, Jan 18, 2013 at 10:55 AM, Oleg Nesterov <o...@redhat.com> wrote: > > > > Or we can do this after wait_task_inactive() but then we need to take > > ->siglock again. > > Yes. We absolutely need siglock, since that would be exactly what > would protect us against signal_wake_up() (which is, I *think* the > only thing that can ever wake up the TASK_TRACED/WAKEKILL cases).
Yes. And thus 4/4 probably should be 1/4. > And we'd need to make sure to re-set the WAKEKILL flag not just in all > the callers of ptrace_check_attach(), but also in the failure case of > wait_task_inactive(). I'm not sure it can actually fail if we cleared > WAKEKILL, but it's all pretty subtle. Afaics it can't fail if we clear WAKEKILL... So 2/4 assumes it should always succeed and adds the warning. > And when we *do* set the WAKEKILL bit again, we should make sure to > wake the task in case the killable signal happened while it was clear. Yes, yes, this is clear. And we need to ensure we can not race with attach-after-detach... > And I agree that this is all pretty scary and generally playing with > another process' 'flags' field is some really nasty business. So I'm a > bit worried about it. Oh yes. And I was going to argue that (a much simpler) change which doesn't allow the tracee to return from ptrace_stop() is better. But then I recalled about set_task_blockstep() and changed my mind (see the changelog in 2/4). Greg, this doesn't look like -stable material. But please let me know if you think 2/4 should be backported. With a couple of simple hacks in PTRACE_DETACH/LISTEN paths we can do this without 1/4 and without changes outside of ptrace.c. But again, probably we shouldn't do this. Please review. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
